1. Field of the Invention
This invention relates to a cylindrical resinous base-body for a photosensitive drum, and a photosensitive drum that includes the resinous base-body. Further, in detail, this invention relates to a cylindrical resinous base-body for a photosensitive drum to be used for an image formation apparatus such as an electrophotographic apparatus, an electrostatic recording apparatus and the like. The resinous base-body is light in weight, easily molded, excellent in dimensional stability, and also superior in image characteristics when used as the photosensitive drum including the base-body.
2. Description of the Related Prior Art
In the conventional electrostatic recording process in an electro photographic apparatus or an electrostatic recording apparatus such as a copying machine, a facsimile equipment, and a printer, an electrostatic latent image is formed by uniformly charging the surface of a photosensitive drum with photoconductive material [for example, ZnO, CdS, Se, OPC (organic semiconductor), amorphous silicon (a-Si), etc.] layer. Then, a toner image is formed by erasing electrostatic charge of the light-irradiated area irradiated imagewisely on the layer from optical system and subsequently supplying a toner on the resultant electrostatic latent image by electrostatic adhesion, and by transferring the resultant toner image to recording media such as paper, photographic paper, etc. or a sheet for an overhead projector, a recorded image is obtained.
As a photosensitive drum to be employed for aforementioned electrostatic recording process, up to now, a drum having a structure shown in FIG. 1 has conventionally been utilized. Namely a drum consists of a cylindrical base-body 1 having good electroconductivity, both ends of the base-body are assembled and fixed with the flanges 2a and 2b respectively and also the surface of the base-body is applied with a photosensitive layer. Further, the drum is supported by the shafts 4a, 4b provided in the main-body of an electrophotographic apparatus and the shafts are inserted into the holes 5a, 5b provided in the both flanges 2a, 2b respectively so as to rotate the drum freely. The drum is rotated by engaging the driving gear 6 provided to the flange 2b with the gear 7 engaged with a driving source such as motor and the like, therefore the drum is driven rotationally.
In a photosensitive drum employed for the aforementioned electrostatic recording processes, a cylindrical or columnar drum base-body made of aluminum alloy obtained by molding has been conventionally utilized because of lightweight, fine machining capability thereof as well as good electroconductivity. Recently however, a cylindrical resinous base-body made of an electroconductive resin composite by injection molding has been utilized too. Such composite is a mixture of a thermoplastic resin and an electroconductive agent such as carbon black. This cylindrical resinous base-body has many advantages as the followings:
Integral molding is applicable for accessories such as the flange or the gear along with base-body part.
It operates with less vibration and with low noise.
Few charge leaks from the cylindrical resinous base-body.
Damping characteristic of the potential regarding the cylindrical resinous base-body is gentle.
Recycling performance of the cylindrical resinous base-body improve.
At this point, there has been desired a more lightweight drum in view of lowering cost, saving electric-power consumption and so on. The aforementioned resinous base-body for photosensitive drums is possible to accomplish a lightweight drum in comparison with a base-body made of aluminum alloy. Unfortunately, it has been further requested to provide a base-body for photosensitive drums with a more lightweight drum so as to save the driving power further; namely lowering cost and saving electric-power consumption has been severely requested to not only photosensitive drums but also materials for electrophotographic apparatuses.
In this case, it is easily possible to achieve weight saving of the aforementioned resinous base-body by providing the base-body with the wall having thinner thickness. It has not been easy, however, to thin the wall since the thinning causes lowering mechanical strength, moldability, dimensional stability and so on. Further, there has been requested, for the aforementioned photosensitive drum, high dimensional precision such as external/internal diameters precision, straightness, perfect-circularity and the like, and also since it is necessary to keep the performance under various application conditions such as high-temperature high-humidity, low-temperature low-humidity and so on, however there has not been realized in any photosensitive drum, up to now, to fulfil the requirements because of the lowered dimensional precision under the environment of high-temperature and high-humidity particularly. In this case, particularly a photosensitive drum is likely exposed for one hour under the high temperature of 120-140xc2x0 C. during a drying step of an OPC(organic semiconductor) photosensitive layer. Therefore, under the condition of the high temperature, the resin is deformed and followed by causing deterioration of external/internal diameters precision and rotational wobble, consequently there leads to a problem of adverse affect to image characteristics.
On the other hand, a metal base-body for photosensitive drums is low in water absorption, therefore there is no change in dimension after long-term usage or usage under high- temperature and high-humidity. Since the change in dimension of the base-body for drums employed aforementioned resin occurs due to water absorption by the resin, there are problems such as formation of image unevenness and the like.
Further, in the case of proceeding the functional cycle of charge, exposure, transfer, discharge, charge, etc., the attenuation characteristic (surface resistance value) of the electric potential on the aforementioned exposure is important. In the case of equipping a photosensitive drum for an image formation apparatus printing at normal speed like 10-15 sheets/min, the surface resistance value is reasonably about 104-105 xcexa9/xe2x96xa1. But, since the drum rotates more speedy in the case of equipping a photosensitive drum for an image formation apparatus printing at higher speed, for example 20-40 sheets/min, image inferior like fog is likely occurred due to the high residual electric potential if the attenuation of the electrical potential on the exposure is not proceeded promptly.
Furthermore, in the case that the aforementioned resin is employed as a base-body for photosensitive drums and the resin is soluble to coating solution forming the photosensitive layer, there is problem of not providing a photosensitive drum being able to form an image of excellent quality. In addition, if adhesion of a photosensitive layer formed is weak, there is another problem of a poor image being caused thereby.
Under the circumstances aforementioned, the object of this invention is to provide a resinous base-body for photosensitive drums being employed to an electrophotographic apparatus; namely the base-body that is superior in moldability, impact strength and dimensional stability, and also easy of weight saving, thinning wall-thickness without lowering mechanical strength as well as moldability. It is another object of this invention is to provide the resinous base-body for photosensitive drums, which enables to form excellent image while controlling occurrence of inferior images. Furthermore, it is still another object of this invention to provide a photosensitive drum including the base-body.
As a result of zealously repeated study by the inventors in order to achieve said objects, this invention was completed to develop a resinous base-body for photosensitive drums having aforementioned excellent performance. This invention provides a cylindrical resinous base-body for photosensitive drums to be used for an electrophotographic process, being made of an electroconductive resin composition and satisfying at least one characteristic selected from the following requirement of from (1) to (7);
(1) a specific gravity of said resin composition is from 1.1 to 1.7,
(2) an apparent viscosity of said resin composition at the apparent shear rate of 104 Sxe2x88x921 is from 1xc3x97102 poise to 3xc3x97103 poise,
(3) an Izot impact value of the said resin composition is 30 J/m or greater,
(4) a water absorption percentage of the said resin composition is 1.5% or less,
(5) a load flexure temperature of the said resin composition is 150xc2x0 C. or higher,
(6) a change in dimension of the external diameter of said base-body is 1.5% or less, and
(7) a surface resistance of said base-body is 1xc3x97103 xcexa9/xe2x96xa1 (ohm/square) or less.
Further, this invention provides a photosensitive drum characterized in that said resinous base-body has a photosensitive layer on the surface thereof, in particular the photosensitive drum being excellent in adhesion with the photosensitive layer.